PhotoVoltaic (PV) solar panels are an important source of power for the electrical grid. Large, megawatt PV installations with PV panels numbering in the tens of thousands are increasingly common. PV panel arrays are typically organized into panel “strings” with each string consisting of from 10 to 20 PV panels connected in series. In a Direct Current (DC) PV panel system, the output of a PV panel string could connect to a central inverter which converts the DC power of the PV panels into Alternating Current (AC) power suitable for the electrical grid.
A known problem of connecting PV panels in series is the differing Maximum Power Point (MPP) currents produced by individual PV panels. The MPP current of a panel (IMPP) is the current corresponding to the panel's maximum power production for a specific level of insolation. A PV panel also has a corresponding MPP voltage. MPP current differences between panels may be caused by one or more of: shading of a particular PV panel, soiling of a PV panel, differences in PV panel orientation, temperature differences or PV panel manufacturing variations. Since all PV panels in a string are series-connected, they must all necessarily be operating at the same current-level. If the panels in a string all have differing MPP currents then it is likely that most of them will not operate at their maximum power points when series connected.
A common solution to the problem of unequal photocurrents is to add DC converters to the output of each PV panel. A DC converter converts power at one DC voltage and current to power at another DC voltage and current. The addition of a DC converter to a panel decouples the panel's output current from the string current. It allows the panel to operate at its own MPP current. For example, for a panel with an MPP current lower than the string current a DC converter could convert power from that lower MPP current (and higher voltage) to the higher string current value (and a lower voltage). A DC converter could thus maximize the power output of a PV panel by allowing it to operate at its MPP independent of string current.